Miguel grew up as the fourth of five children in an Irish-Mexican family. One of his closest friends growing up was local tomboy Kay Bennett, who secretly had feelings for him and wanted to be his girlfriend; he unknowingly had romantic feelings for Kay, due to Miguel only seeing her as a friend at the time. However, in the summer of 1999, Miguel met the mysterious Charity Standish and it was love at first sight, much to Kay's dislike.

Over the next five years, Kay schemed and plotted to take down Charity and have Miguel all to herself. She even succeeded in getting pregnant with Miguel's child by using Charity's essence to make him think she was her cousin, and giving birth to a baby girl, Maria, in July 2003. But this wasn't enough to land Miguel for good, as Charity left town a year later, and Miguel soon followed after her, leaving Kay as a single mother. Months later, Miguel returned to town, rushing to his daughter's aid much to Kay's delight. Miguel acted as a loving father to Maria and a loving friend to Kay, while helping his family deal with his brother's recent death. Miguel finally realized his feelings for Kay while bonding with their daughter, Maria, however he was secretly trying to track down Charity whereabouts. Miguel finally realizes that he must find the real woman he loves, Charity and left Kay and Maria behind Harmony in early January 2005.

Just as Kay finally started to get over Miguel and became engaged to Fox Crane, Miguel returned to town in February 2006 at the request of Valerie Davis, who was working with Ivy Winthrop to break up Fox and Kay. Miguel announced that he had decided to give up on his search for Charity and would stay in Harmony so that Maria would have her father back in her life. And although Kay wouldn't admit it out loud, her feelings for Miguel were returning. The relationship between Miguel and Kay took another twist when Miguel fell off a fishing boat and drowned, but was rescued by a mysterious, young woman named Siren, who was actually a mermaid created by Endora Lenox, Fox's half-sister. Siren was instantly in love with Miguel, and Miguel didn't mind having a relationship with the attractive and playful Siren. But when Miguel and Kay were unexpectedly electrocuted, Kay got amnesia and believed she was engaged to Miguel. She had no idea that Fox was her fiancé. This development infuriated Fox and Siren, but Miguel decided to play along, believing it would help Kay bring her memory back.

Eventually, Kay got her memory back, which caused Miguel to discover how much he actually loved Kay. Siren attempted to put Miguel under the mermaid's curse. However, Kay prevented it by telling Miguel she loved him and broke him out of the trance. Soon afterwards, Endora zapped Siren into a fish tank after Fox complained that she complicated his relationship with Kay. Miguel was sure that Kay had feelings for him, and he finally won her over Fox. Miguel and Kay had plans of getting married and getting their own home. Fox who couldn't get over the fact that Kay was leaving him for Miguel, faked an illness so Kay would feel sorry for him and stay with him. This led to their marriage on January 10, 2007. Miguel became suspicious that Fox's illness was fake, but he wasn't able to prove it to Kay. Fox even managed to fake a hit and run blamed Miguel for the accident (with the help of his father Julian and Spike). Eventually, Fox's lies were exposed, and Kay separated from Fox.

When the forces of darkness came to kidnap Endora on September 7, 2007, Kay was forced to tell Miguel that she, Tabitha, and Endora are all witches. Miguel was shocked, but was determined to rescue Endora; however, his efforts only resulted in his own abduction. Eventually, he and Endora returned to Earth on Christmas Eve, where he found that Fox was dead and he and Kay were free to move on together.

After a while Miguel began to feel like he was losing his mind because he couldn't remember where he had been. When he tried to call himself into an insane asylum, Kay used her magic and accidentally repaired his memory of him being in Hell, which also resulted him to remember his fiancée, Endora and Tabitha are all witches. With that happening, he made Kay take a sacred oath to never use magic again or else they could not be together. Kay agreed. But then Miguel realized they would have to make Tabitha stop using magic as well. Tabitha refused to give up on magic until Miguel blackmailed her with a letter he wrote and hid about her being a witch, for if anything bad was to happen to him she'd be exposed. He explained to Tabitha that she was a nice witch but if magic was to stop, all the evils of Harmony would stop as well. She agreed to give up magic, but secretly vowed she would find that letter and turn Miguel into a toad.

On July 21, 2008, Miguel and Kay became husband and wife.

After Miguel and Kay got married, the volcano, Mt. Harmony erupted in Harmony. Miguel gave Kay permission to use magic, figuring it would do some good for a change. When Harmony was saved, Miguel finally gave in and said he was okay with Kay using magic and being a witch.